MSUD, Maple Syrup Urine Disease

This is part three in the series for Metabolic Disease Awareness Week. It focuses on Maple Syrup Urine Disease or as it is commonly called MSUD.

MSUD has an incidence rate of 1 in 250,000 people in the UK (this is similar to the US): it is inherited in a autosomal recessive manner. This means that the parents of the affected child carry a genetic trait that causes MSUD. There is a 25% chance of having a child with MSUD if both parents are carriers.

People need proteins to live and grow however a person with MSUD is unable to process the amino acids called leucine, isoleucine and valine: these are commonly known as the branch chain amino acids (BCAAs). A person with MSUD will have high levels of these BCAA in the blood which penetrates and damages the brain.

There are 5 different types:

Classic.
Intermediate.
Intermittent.
Thiamine sensitive.
Dihydrolipoil deshydrogenase deficiency.

We will focus on the classic type at this stage, which is the most severe.

The symptoms are characterised by the sweet smell of urine. Typically an untreated baby will experience poor feeding (unable to suck), lethargy, vomiting, rigid muscle tone and seizures. If left untreated it can lead to permanent mental retardation, coma and even death.

Early diagnosis with good metabolic control through dietary management will help to minimise the risk of brain damage. Such a diet will restrict the protein intake: mainly the branch chain amino acids (BCAAs).

In the UK there is no neonatal screening for MSUD: it is screened in about half the States of the USA and some other countries. It is imperative that special medical attention is sought after if a child experiences the symptoms described.

There is no cure for MSUD and an individual should remain on diet for the remainder of their life.